The physical and chemical nature of elemental selenium in the environment

硒（Se）是目前北美重要的无机污染物。它是从一些主要的工业过程中意外排放到水生环境中的，包括燃煤发电厂、炼油厂和各种类型的采矿作业（如煤、金和铀）。在一些接收环境中，人们担心硒排放产生的生态毒理学效应，这可能导致硒在水生生物中的生物积累，并对水生鸟类和捕食性鱼类的生殖产生影响，最终危及整个当地人口的生存。 美国环境保护署和加拿大环境部正在重新评估并（很可能）降低其目前的环境硒水质标准。因此，大多数工业操作目前正在评估或安装除硒系统。细菌还原反应器，模仿发生在环境水体中的过程时，硒被删除到沉积物，是目前最流行的类型的处理系统考虑/安装。这些系统应该将可溶性Se化合物转化为不溶性元素Se，其从水中除去并与固体残留物一起处理。虽然这些处理系统通常在降低工艺沃茨中的总硒浓度方面非常有效，但一小部分硒通过这些系统，并且仍然可能引起生态毒理学问题。特别令人感兴趣的是所释放的硒的化学性质，并且初步研究表明，其中一些硒可能以具有非常小的颗粒尺寸的悬浮胶体元素硒的形式存在。然而，目前没有分析方法可用于测量胶体元素Se，或表征其相对于分子组成或粒度的性质。 在拟议的研究计划中，我们将开发这样的方法，然后在实验室研究中量化和表征由生物还原以及化学过程产生的元素硒，然后在自然水沉积物系统以及工业除硒工厂中。我们的研究结果将首次确定胶体元素Se是否以及以何种确切形式在这些过程中发挥作用。这将为评估从工业处理操作排放到环境沃茨中的元素硒的命运奠定基础，因为元素硒可能对生物体不可用，并将迅速沉积，但也可能能够转化回水柱中的可溶性硒物质。对于工业利益相关者，我们的研究将提供评估生物还原是否是长期正确的处理技术的一部分，而对于加拿大公众，它将有助于确定这种处理过程中持续的低水平硒排放是否对水生生物构成危险。

Selenium (Se) is an inorganic contaminant of high current importance in North America. It is discharged accidentally into the aquatic environment from some major industrial processes, including coal-fired power plants, petroleum refineries and various types of mining operations (e.g. coal, gold and uranium). In some receiving environments, there is concern about ecotoxicological effects arising from Se discharges, which may lead to Se bioaccumulation in aquatic organisms, and to reproductive effects in aquatic birds and predatory fish that can ultimately endanger the survival of entire local populations. The US Environmental Protection Agency and Environment Canada are in the process of re-evaluating and (most likely) lowering their current ambient Se water quality criteria. Consequently, most industrial operations are currently evaluating or installing Se removal systems. Bacterial reduction reactors, which mimic the processes occurring in ambient water bodies when Se is removed to the sediments, are currently the most popular type of treatment system considered/installed. These systems are supposed to convert soluble Se compounds into insoluble elemental Se, which is removed from the water and disposed of with solid residues. While these treatment systems are often very effective at lowering the total Se concentration in the process waters, a small fraction of Se passes through these systems, and may still raise ecotoxicological concerns. Of particular interest is the chemical nature of the released Se, and preliminary studies suggest that some of this Se might be present in the form of suspended colloidal elemental Se with very small particle size. However, there are currently no analytical methods available to measure colloidal elemental Se, or characterize its properties with respect to molecular composition or particle size. In the proposed research program, we will develop such methods, and then quantify and characterize elemental Se generated by biological reduction, as well as chemical processes, in laboratory studies, and later on in natural water-sediment systems, as well as in industrial Se removal plants. The results of our studies will determine for the first time if, and in what exact form, colloidal elemental Se plays a role in these processes. This will lay the foundation for assessing the fate of elemental Se discharged from industrial treatment operations into ambient waters, since it is possible that elemental Se is unavailable to organisms and will sediment rapidly, but may also be able to convert back into soluble Se species in the water column. For the industrial stakeholders, our research will provide part of the assessment whether biological reduction is the right treatment technique in the long term, while for the Canadian public, it will help determine if continued low-level Se emissions from such treatment processes pose danger to aquatic organisms.